def bfs():
    # 1. 初始化队列和状态
    queue = [1]

    # 2. while queue不为空
    while queue:
        # 3. 队顶元素出队
        t = queue.pop(0)
        if t not in graph: continue    # ！！！注意：判断如果元素t不存在相邻节点(即出度为0)，则跳过
        # 4. 遍历，满足条件的节点入队
        for i in graph[t]:
            if not st[i]:
                st[i] = True    # 出错：忘记更新状态导致死循环了
                queue.append(i)
                if d[i]==-1:
                    d[i] = d[t]+1
    print(d[n])  


# 1. 输入示例
n, m = map(int, input().split())

# 2. 图的存储模板(有向图)
graph = {}
for i in range(m):
    a,b = map(int, input().split())
    if a not in graph:
        graph[a] = [b]
    else:
        graph[a].append(b)
# 3.初始化状态
st = [False for i in range(n+1)]
st[1] = True
d = [-1 for i in range(n+1)]    # 用来存储每个点到节点1的距离
d[1] = 0

# 4. bfs搜索
bfs()